As a support bearing which rotatably supports a rotation shaft of a motor (hereinafter, may be simply referred to as a “bearing”) in a motor device for rotating a disk-shaped recording medium, an oil-impregnated sintered bearing which is capable of rotating the rotation shaft at a high speed without oil supply is often used. In order to smoothly rotate the rotation shaft which is supported by the oil-impregnated sintered bearing, a clearance that an oil film can be formed is required between the rotation shaft and an inner peripheral face of the bearing. However, the rotation shaft may rattle due to the clearance and thus a turntable on which a disk-shaped recording medium is placed may be vibrated. The vibration of the turntable causes a reading error (so-called sound skipping or the like) on a signal recording face of a disk-shaped recording medium in an optical pickup device or a magnetic head device on which the motor device is mounted. Especially, in an optical pickup device which is mounted on a vehicle, since vibration is applied to the vehicle itself, a reading error may be often occurred.
In order to prevent this problem, for example, as described in Japanese Patent Laid-Open No. Hei 8-87825 and Japanese Patent Laid-Open No. 2002-374651, a structure has been known in which a side pressure is applied to the rotation shaft of the motor in a direction intersecting an axial direction of the motor as a means for restraining vibration of the rotation shaft during driving of the motor. According to this type of the side pressure applying mechanism for a motor, an urging member (torsion coil spring in the former Patent Literature and a wire spring in the latter Patent Literature) is abutted with an outer peripheral face of a side pressure bearing (ring member in the former Patent Literature and slip ring in the latter Patent Literature) so that a pressing urging force is applied to the side pressure bearing in a direction intersecting the axial direction and, as a result, a side pressure is applied to the rotation shaft through the side pressure bearing. In this manner, since the rotation shaft is pressed against the inner peripheral face of the oil-impregnated sintered bearing, rattling of the rotation shaft due to the clearance is restrained and occurrence of a reading error caused by vibration of the turntable is prevented.
In the side pressure applying mechanism for a motor described in the former Patent Literature, the urging member (torsion coil spring) is abutted with the outer peripheral face of the side pressure bearing (ring member) to urge the side pressure bearing in a direction substantially perpendicular to the axial direction of the rotation shaft. However, in a case that this structure is used in an optical pickup device for a vehicle or the like, when the urging member which is abutted with the outer peripheral face of the side pressure bearing is moved up and down in the axial direction of the rotation shaft of the motor by a disturbance such as a sudden impact, the urging member is disengaged from the outer peripheral face of the side pressure bearing and, for example, the urging member may climb on an upper face of the side pressure bearing (hereinafter, the state where the urging member has climbed on the upper face of the side pressure bearing may be simply described as “climbing of the urging member (on the side pressure bearing)”.
On the other hand, in the latter Patent Literature, a structure is described in which a protruded part that is protruded from an upper end part to an outer side in a radial direction is formed on the side pressure bearing (slip ring). According to this structure, the urging member (wire spring) which is abutted with the outer peripheral face of the side pressure bearing is located under the protruded part and thus the climbing of the urging member on the side pressure bearing can be prevented. However, in this structure, since the urging member is caught by the protruded part of the side pressure bearing, when the urging member is moved up and down by a disturbance such as a sudden impact, the side pressure bearing is also moved up and down together with the urging member (the urging member moves so as to lift the side pressure bearing up), which may cause a situation that the side pressure bearing is abutted with the turntable to occur an abnormal noise. Further, the protruded part is difficult to secure a sufficient strength and a cost for forming the side pressure bearing is increased.